P and N channel transistors have been found to have improved performance by use of strained semiconductor material in the channel. N channel transistors benefit from more tensile stress, whereas P channel transistors benefit from compressive stress. A number of techniques have been proposed to achieve one or both of these stresses. One of the difficulties is enhancing the stress for both the N and P channel transistors. Another issue is achieving an enhancing stress while not introducing detrimental defects. Another issue is providing the optimum direction for the stress. For example, P channel transistors benefit more from an increase in compressive in the channel length direction than from an increase in compressive stress in both the channel length and channel width direction. Another issue is proper material choices for the P and N channel devices. N channel devices are generally better if they have a silicon channel rather than a germanium or silicon germanium (SiGe) channel because SiGe has lower electron mobility than silicon.
Thus, there is an need for a device that has the desired benefits that can be made in a process that improves on one or more of these issues.